Five-year growth response of western red cedar, western hemlock, and amabilis fir to chemical and organic fertilizers
The hypothesis that growth responses of conifers to application of organic fertilizers are of longer duration than responses to chemical fertilizers was tested in two trials on northern Vancouver Island. Both trials were in 10-year-old plantations of conifers on a salal-dominated cutover known to have poor N supply. In Trial 1, western red cedar (Thuja plicata Donn ex D. Don), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and amabilis fir (Abies amabilis (Dougl.) Forbes) were treated with municipal biosolids at 542 kg N·ha-1 and 162 kg P·ha-1 or ammonium nitrate and triple superphosphate at 225 kg N·ha-1 and 75 kg P·ha-1. Height increments in the 5 years following applications were two to five times greater in plots treated with either biosolids or fertilizer than in untreated plots. In Trial 2, western red cedar was treated with fertilizer at 225 kg N·ha-1 and 75 kg P·ha-1 or the following organic amendments at 504-610 kg N·ha-1: biosolids, biosolids and pulp and paper sludge, fish silage and wood ash, fish silage with wood ash and pulp and paper sludge, and wood ash alone. Height increments in the 5 years following applications were similar in all treated plots (except wood ash alone). These experiments provided no evidence for sustained growth responses in plots treated with organic fertilizers compared with those treated with chemical fertilizer.